Sitting
on the hill of an alien world millions of miles from home, a hardy
NASA robot celebrates an anniversary today - one year on the planet
Mars.

The Mars rover Spirit has
come a long way since it hurtled down through the planet's atmosphere and came
to a bouncy, airbag-protected stop at
Gusev Crater on Jan. 3, 2004. It has survived more than four times its
initial 90-day mission, driven miles across the Martian landscape and weathered
a red planet winter
only to scale hills for its human handlers.

"I never, ever would have imagined
that I would have the opportunity to be standing here a year later and say we're
back and still on Mars," said NASA's top administrator Sean O'Keefe today during
a press conference at the Jet Propulsion Laboratory (JPL) in Pasadena,
California. "What the exploration team has done in the last 12 months is
absolutely nothing short of remarkable."

O'Keefe spoke during
a full day of storytelling, reflection and news conferences
commemorating Spirit's first year exploring Mars. Mission managers,
scientists and engineers clapped loudly in a JPL auditorium as O'Keefe blew
out the birthday candle atop Spirit's birthday cake.

"This has been a stressful
year...but both rovers have been very successful," said Jim Erickson, project
manager for the rover mission at JPL, during the press briefing. "Bad things
could happen to us at any time, but as long as we have them we're going to keep
using them to the best of their abilities."

A continuing
mission

Spirit continues to return
science information from the Columbia Hills, after driving 2.4 miles (4
kilometers) from its Gusev Crater landing site. Scouring those hills has given
Spirit - and researchers - more evidence
that water shaped Mars' past. Meanwhile, on the other side of Mars at Meridiani
Planum, Spirit's robotic twin Opportunity is studying its own heat
shield while it seeks to dig more details on the area's watery
past.

"It's astonishing to me how
well it's going," said Steve Squyres, principal investigator for the Mars
Exploration Rover (MER) project from Cornell University, of the mission before
today's anniversary. "They're tough machines built by a fantastic
team."

During today's briefing,
Squyres said that working with Spirit and Opportunity has been "the adventure of
a lifetime" for both himself and the mission team.

Some hitches on the
way

A software problem
dogged Spirit in the early weeks of its mission when it fell silent for a
period, but engineers were able to work through the glitch and resume the
rover's science
mission.

"That was waiting to bite
us," Squyres said of the glitch, which involved Spirit's flash memory and
required updated software to fix. "If Opportunity had landed first, it would
have had the same problem."

Spirit has experienced
other quirks, such as a finicky wheel
that has left it dependent on only five of its six wheels to rove about Mars.
But the glitch has not prevented to rover from slowly making its way up "Husband
Hill" in the Columbia Hills.

"Spirit is our tough,
hardworking robot," Squyres said, adding the rover is scratched and dusty.
"Opportunity looks like she just came off the showroom floor, clean and
pretty."

Squyres and other mission
team members have become so adept at handling Spirit and Opportunity from Earth,
they no longer need to congregate together at NASA's Jet Propulsion Laboratory
(JPL) to plan out each moment of each rover's day. Instead, telephone and video
conferences allow researchers to operate the rovers remotely.

"From an engineering
standpoint, you really have to tip your hat," JPL's Matt Golombek told
SPACE.com. "These rovers were designed for a lifetime of three months
and now it's not clear when they're going to stop."

Looking
ahead

Mission scientists
said the next stop for Spirit is a region dubbed Cumberland Ridge where they
hope the rover will find more rocks akin to the rock target "Wishstone", a
phosphorous-rich object that unlike the surrounding Columbia Hills
material.

"The first message is that
this is dramatically different than anything we've seen," Squyres
said.

Meanwhile, Opportunity will
continue its heat shield studies and hopefully return information that could
hopefully help engineers design better versions for future spacecraft. Once
finished, Opportunity is expected to hopscotch across Merdiani Planum, moving
from crater to crater until it reaches a circular feature dubbed "Vostok",
which may or may not be an actual crater.

"We don't know if it's a
strangely eroded impact crater or what," Squyres said of the
object.